The present invention generally relates to firefighting equipment, and more specifically, to compressed air foam systems used to mix a stream of water with foam chemical and air to produce a water/foam/air mixture for firefighting purposes. Even more specifically, the present invention relates to systems and methods for controlling the introduction of air into the water and foam chemical mixture.
The addition of foaming agents to firefighting water streams is known and can be particularly useful for fighting fires, for example, fires in industrial factories, chemical plants, petrochemical plants and petroleum refineries. The use of compressed air firefighting foam requires that air and a foam concentrate be mixed and added at constant proportions to the water stream. When the foam extinguisher solution is delivered, the foam effectively extinguishes the flames of chemical and petroleum fires as well as Class A materials which would otherwise not be effectively extinguished by the application of water alone.
It is important that the foam concentrate be added to the water stream in the appropriate proportion. When an excessive amount of foam concentrate is added, a lower fire-extinguishing quality can result due to an increased foam viscosity which limits the flowability of the foam and the ability of the foam to be spread on the fire. Further, the addition of excessive amounts of concentrate to the water stream increases the cost of the use of the foam and the frequency at which the foam concentrate supply must be replenished at the scene.
It is also important that the amount of air added to the water and foam chemical mixture be properly regulated, i.e. added in the appropriate proportion. The amount of air introduced into the water and foam chemical mixture is controlled to achieve the desired consistency of foam. Firefighting foam that is either too watery due to insufficient air or too dry due to excessive air is less effective at fighting fires and may even be dangerous. The condition in which an excessive amount of air is introduced with the nozzle closed to create the foam is commonly referred to as air packing or just packing of the hose.
As the nozzle operated by the firefighter at the end of the hose line is closed, extra air or water will tend to flow into the hose line depending on which one has a higher pressure. This may contribute to an unbalanced foam mixture. Existing firefighting foam systems have had difficulties in maintaining the pressures of the water and air equal to each other. Some firefighting foam systems, such as the CAFSMaster available from Hale Products, Inc., Conshohocken, Pa., recognized this and actually proportion the air introduced into the water using a venturi device. However, existing air proportioned systems generally increase the size and weight of the firefighting foam system. Other firefighting foam systems use an operator to control the introduction of air by constantly making manual adjustments to maintain a desired foam mixture.
Existing firefighting foam systems have attempted to control the introduction of air by adjusting an air valve on the discharge side of an air compressor used to supply air to generate the foam. However, the air compressor continues to place an unnecessary load on the engine used to provide power for firefighting equipment. Engine power that would otherwise be available for other firefighting activities is reduced due to the unnecessary air compressor load. Also, the air compressor continues to burn fuel and experience wear and tear unnecessarily.
In addition to controlling the introduction of air into the water and foam chemical stream to achieve a desire foam consistency, it is also desirable to reduce the air flow or completely shut off the air flow under certain conditions. For example, if foam chemical is not being added to the water then air should be prevented from being introduced into the water stream. Air and water do not mix under pressure. If air is added to the water without the foam chemical the unmixed air and water will cause violent surging of the firefighting hoses, commonly called slug flow. The violent surging action can be sufficiently forceful to knockdown or injure the firefighter who is operating the fire hose.
Examples of existing foam generating systems can be found in U.S. Pat. No. 5,096,389 to Grady, entitled Compressed Air Foam Discharging Apparatus, and U.S. Pat. No. 5,582,776 to Crawley et al., entitled Apparatus for Generating Foam.
In view of the existing firefighting foam mixing equipment, there are needs to have new compressed air foam systems. There are particular needs for new compressed air foam systems which control the introduction of air into the mixture to generate the foam.
The present invention provides compressed air foam systems which generate compressed air foam, for firefighting, for example. The new compressed air foam systems increase safety for relatively small, simple foam generation units by employing a flow sensing element into the foam proportionor design to regulate and turn the air flow from the air compressor off when water flow is shut off. In one embodiment of the present invention, a flow sensor senses the position of a piston in a foam proportionor which provides a signal indicative of water flow. The control system actuates an air flow regulator on the air intake to an air compressor which controls the amount of air mixed into the stream or even shuts off the air flow. Accordingly, the present invention includes new air flow control systems for compressed air foam systems.
Furthermore, the air flow can be shut off when various conditions occur, for example, the error conditions of: out of foam chemical, foam system failure, and foam proportioner in an off condition when attempting to generate compressed air foam.
The compressed air foam system of the present invention is a self-contained system that fits in a cabinet on a side of a fire truck and can be retrofitted to a fire truck. The compressed air foam system may be small enough in size to fit in a European fire truck compartment, such as a DIN 8 kVA generator compartment, commonly found in European fire trucks.
Compressed air foam technology further improves the firefighting capacity of water and foam chemicals by producing a higher energy stream that penetrates the fire and by producing a higher quality foam bubble structure than is obtainable by other methods. As an additional benefit, compressed air foam lines are lighter than water lines and place less stress on the firefighters and allow a greater degree of mobility. This facilitates reduced water damage, quicker fire knockdown and a resultant xe2x80x9csaferxe2x80x9d environment for both the firefighters and potential victims.
Objects and advantages of the present invention will become apparent upon reading this disclosure including the appended claims and with reference to the accompanying drawings. The objects and advantages may be desired, but may not necessarily be required to practice the present invention.